STS083-712-063

Northern half of Long Island, Bahamas. The vivid blues of the Bahamas stand out from space. Long Island and Great Exuma Island, which extends from the west north west into the photo, is on the eastern side of the Great Bahama Bank and form the borders of Exuma Sound. This photograph provides a rare opportunity to observe a natural chemical laboratory at work. Limestone of quite a different sort from that forming the Great Barrier Reef is actually in the process of formation. Long Island itself is little more than a sandbar rising just a few meters (about 30 to 50 meters) above sea level but it separates the deep, dark blue waters of the Atlantic on the right from the 10-meter (33 feet) shallows of the Great Bahama Bank (left). Details of the topography of the bank are visible through the clear waters. The shallow waters are warm and become extremely salty. Crystals of aragonite, a calcium carbonate mineral, are precipitated and formed into spherical sand-sized oolites as the tidal currents swirl back and forth. Lithification of the carbonate sands produces an oolithic limestone. Although the water is warm and clear, corals do not live in the shallows, probably because of the elevated salt content. Although chemically similar, the oolithic limestone forming Long Island is very different from coral reef limestone. An airfield is visible at the northern and central (bottom of photo) part of the island.